Tap changer movable contact



July 17, 1 962 A. WILSON, JR.. ETAL 3,045,090

TAP CHANGER MOVABLE CONTACT Filed May 8, 1959 U :it

Stes

Filed May 8, 1959, Ser. No. 811,829 Claims. (Cl. 200166) This invention relates to stationary induction apparatus and in particular to tap changers for stationary induction apparatus.

Tap changers are conventionally used to adjust the turn ratio of transformers for the purpose of maintaining constant voltage at selected points on alternating current power systems. Since the turn ratio of the transformer must be changed without interfering with the load, in order to move from transformer tap A to tap B it is neecssary to close the circuit to tap B before opening the circuit at tap A. For the purpose of shunting the load current from one winding tap to the next, two individually operable contacts are utilized so that one of the contacts will at all times maintain an uninterrupted electrical circuit from the input to the output of the transformer and a preventive autotransformer is provided to limit the circulating current to a safe value during the interval that two adjacent taps are bridge One compact tap changer arrangement by which 33 operating positions can be obtained includes a 9-contact dial switc a double-throw transfer switch, and means for moving the two contacts sequentially over the nine stationary contacts eight of which are connected to individual transformer taps. The stationary contacts are uniformly spaced on the circumference of a circle so as to permit 32 steps of the movable contacts in two revolutions, and plusminus voltage control is obtained by reversing the tapped winding by the double-throw transfer, or reversing, switch so the same tapped winding is utilized in both buck and boost position. In one common form of such high speed tap changing switch, the radially inward ends of the movable contacts maintain continuous high pressure electricalengagement with metallic collector rings connected to opposite ends of the preventive autotransformer. The movable contacts are resiliently urged into highpressure engagement with the stationary con tacts to provide low contact resistance and are operated at relatively high speed between stationary contacts to provide fast contact break and thus minimize contact erosion and pitting due to arcing. I spring drive in such high-speed tap changer with a motor to store energy in the spring and to release the spring to snap themovable contacts from one stationary contact to the next, whereby the duration of the arc is greatly reduced, the amount of burning of contacts is lessened, and the life of the contacts is increased. One defect of such prior art high speed tap changing switch, however, is that considerable burning and pitting of the collector rings occurs which requires frequent inspection and maintenance of the tap changer and occasional replacement of the collector rings.

It is an object of the invention to provide an improved movable contact for a tap changer having collector rings which minimizes the pittin burning, and erosion of the collector rings.

It is a further object of, the invention to provide an improved tap changer rotatable contact which is adapted to compensate for any misalignment of the stationary contacts and to sequentially engage at high speed a plurality of stationary contacts with high pressure contact but with minimum bounce and burning.

These and other objects and advantages of the invention will be more readily apparent from the folowing detailed It is common to employ a atent 3,045,090 Patented July 17, 1962 description when taken in conjunction with the accompanying drawing wherein:

FIG. 1 is a partial sectional view through a tap changer having rotatable contacts in accordance with the invention, only one rotatable contact being illustrated and being shown in side view;

FIG. 2 is a sectional view through the rotatable contact; and

FIG. 3 is a front view of the rotatable contact.

Referring to the drawing, the tap changer includes nine stationary contacts 11 arranged in a circle and including a first set of coplanar stationary contact members 11A spaced axially from a second set of coplanar stationary contact members 11B. The corresponding contact members 11A and 11B are electrically commoned and spaced apart by metallic sleeves 12 surrounding metallic studs 13 secured to metallic contact support member 14. Contact support member 14 is positioned against an insulating collar 15 and is secured to a metallic stud 17 which extends through an insulating panel 18 which forms an oil-tight partition between the transformer and the compartment (not shown) housing tap changer 1i). Nuts threaded on stud 17 rigidly mount the stationary contacts 11 on the panel 18, and electrical leads 19 secured to the studs 17 are connected to taps on a tapped series winding (not shown) of the transformer,

A rotatable contact 20 is adapted to sequentially engage stationary contact members 11A and to also remain in continuous high pressure electrical contact with a metallic collector ring 23 formed by a circumferential flange on a conical metallic member 24 mounted on panel board 18 and connected by an electrical lead 25 to one end of a preventive autotransfor-mer (not shown). Collector ring 23 is in the plane of the stationary contact members 11A. A rotatable contact identical to contact 20 adapted to sequentially engage stationary contact members 11B is omitted from the drawing in order to shorten the description and to facilitate the understanding of the invention. Contact 20 is carried on a bifurcated insulating switch arm which issecured by suitable means such as rivets to a radially extending flange 31 on a rotatable shaft 32.

Thewords axially, radially, and circumferentially are used throughout the description with reference to the axis of shaft 32 which coincides with the center of the circle about which the stationary contacts 11 are arranged. Rotatable contact 20 includes a pair of opposed, generally radially extending, flexible, laminated copper shunts 37. Laminated copper shunts 37 are preferably constructed by spirally winding thin copper strip and flattening the spirally wound loop. Laminated copper shunts are known for electrical connections, but they are commonly formed by reverse folding the thin copper strip a plurality of times to the desired thickness, thus requiring the electrical current to transfer from lamination to lamination perpendicular to the plane of the flat copper strip. The spirally-Wound-and-flattened laminated copper shunts 37 permit transfer of electrical current both along the thin copper strip, as well as from lamination to lamination, in a direction perpendicular to the plane of the laminations.

The radially outward end of each copper shunt 37 abuts against a metallic front swivel plate 38 and is secured thereto by rivets which also affix an arcing contact button 39 to the radially outer end of shunt 37. The radially inward end of each copper shunt 37 abuts against a metallic rear swivel plate 46 and is securedthereto by a rivet which also aflixes a contact button 41 to the radially inward end of the shunt 37. An arcuate portion 43 intermediate the ends of each copper shunt 37 is disposed against the convex portion 44 of a metallic thrust piece 45 having generally circumferentially extending arms secured by bolts 47 to the bifurcations of the switch arm so.

Each front swivel plate 38 has depending, circumferentially spaced apart bent-over cars 49 disposed on opposite sides of the thrust piece 45. Each rear swivel plate i? has upwardly extending, circumferentially spaced apart, bent-over ears 5t disposed outwardly of the ears 49 on front swivel plate 38. Hinge pins 52 extend circurnferentially through clearance holes in the thrust piece 45, in the bentover cars 49 on front swivel plate 33, and in the bent-over cars 50 on rear swivel plate 40, and snap rings 53 fitting within circumferential grooves adjacent the ends of binge pins 52 hold the elements in a unitary assembly. As discussed in detail hereinafter, the front and rear swivel plates 38 and 40* secured to the flexible copper shunt 37 and to the contact buttons 39 and 41 are thus hinged, or pivoted, about hinge pins 52, and inasmuch as the pins 52 are parallel to the plane of the stationary contact members 11A and tangential to a circle concentric with the circle about which the stationary contacts 11 are arranged, the contact buttons 39 and 41 are, in efiect, hinged to move transverse of the plane of the stationary contact members 11A.

A pin 60 radially outward from thrust piece 45 extends axially through clearance holes in the opposed copper shunts 37 and in the front swivel plates 38- secured thereto. Compression springs 61 surrounding pin 64) between the front swivel plates 38 and washers disposed against snap rings 63 fitting within circumferential grooves adjacent the ends of pin 60 resiliently urge the arcuate portion 43 of the copper shunts 37 against the convex portion 44 of thrust piece 45 and also resiliently urge the front swivel plates 38 toward each other and the arcing contacts 39 against opposite sides of the stationary contact members 11A. A sleeve spacer 65 surrounding pin 60 between the front swivel plates 38 maintains the arcing contacts 39 at the optimum separaion to permit smooth entry of the stationary contact members 11A between arcing buttons 39 and to also assure high pressure engagement with stationary contact members 11A. The spacer 65 maintains the copper shunts 27 a distance apart greater than the axial dimension of the thrust piece 45, and this construction permits the rotatable contact to pivot as a unit in a direction transverse to the plane of contact members 11A. Thus not only can the individual arcing contacts 39 pivot about the hinge pins 52 to compensate for any misalignment of stationary contact members 11A from their common plane, but also the entire rotatable contact 20 can move as a unit transverse to this plane to compensate for stationary contact misalignment.

An axially extending pin 70 disposed radially below thrust piece 45 protrudes through clearance holes in the rear swivel plates 40 and in the copper shunts 37. Helical springs 71 surrounding pin 70 between the rear swivel plates 40 and washers 72 positioned against snap rings 74 fitting in circumferential grooves adjacent the ends of pin 7 (l resiliently urge the rear swivel plates 40 toward each other and thus urge the contact buttons 41 against opposite sides of collector ring 23. Rear swivel plates 40 are pivoted about hinge pins 52 for movement transverse cf the plane of the stationary contact members 11A and collector ring 23. Inasmuch as both front swivel plates 38 and rear swivel plates 40 are pivoted about hinge pins 52 for movement transverse of the plane of the stationary contact members 11A, and, further since contact buttons 39 and 41 are electrically connected through flexible copper shunt 27, it will be apparent that any axial movement of arcing contacts 39 when brought at high speed into engagement with a stationary contact member 11A will not be transmitted to contact buttons 41. Consequently, no bounce of the contact buttons 41 relative to collector ring 23 occurs due to the arcing contact buttons 39 engaging the stationary contact members 11A, and burning and pitting of the collector ring 23 and the contact button 41 in engagement therewith is minimized. It will be appreciated that the disclosed rotatable contact eliminates the problem of collector ring and electrical contact burning and pitting characteristic of prior art tap changers and thus obviates the necessity of frequent inspection and maintenance of the tap changer,

While only a single embodiment of the invention has been illustrated and described, many modifications and variations thereof will be apparent to those skilled in the art, and consequently it is intended in the appended claims to cover all such modifications and variations which fall within the true spirit and scope of the invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

l. A tap changer contact adapted to sequentially engage a plurality of coplanar stationary contacts arranged in a circle and to electrically connect said stationary contacts to a collector ring concentric with said circle and radially inward from said stationary contacts, said tap changer contact including a pair of generally radially extending, elongated, flexible members of high electrical conductivity, a support member disposed between said flexible members intermediate the ends thereof and carrying said flexible members and being adapted to be moved in a arcuate path concentric with said circle, a pair of opposed arcing contacts, one being secured adjacent the radially outward end of each flexible member, a pair of opposed contact buttons, one being secured adjacent the radially inward end of each flexible member, a pair of plate members, one abutting the radially outward end of each said flexible member on the side thereof opposite said arcing contact, means for pivotally mounting said plate members on said support member for movement transverse of the plane of said stationary contacts, means for resiliently urging said plate members toward each other and said arcing contacts into engagement with said stationary contacts, and means for resiliently urging said contact buttons toward each other and into engagement with said collector ring.

2. A tap changer contact adapted to sequentially engage a plurality of coplanar stationary contacts arranged in a circle and to electrically connect said stationary contacts to a collector ring concentric with said circle and radially inward from said stationary contacts, said tap changer contact including a support member adapted to be moved in a circular path concentric with the circle about which said stationary contacts are arranged, said support member having a pair of circumferentially extending support arms and a pair of axially projecting convex surfaces, a pair of elongated, laminated, generally radially extending shunts of high electrical conductivity, each shunt having an arcing contact secured to the radially outward end thereof and a contact button secured to the radially. inward end thereof and a concave portion intermediate its ends fitting over said convex surface of said support member, a pair of binge pins extending circumferentially through said support member, first swivel plates secured to the radially outward end of said shunts on the side thereof opposite said arcing contact and being pivotally mounted on said hinge pins for movement transverse of the plane of said stationary contacts, second swivel plates secured to the radially inward end of said shunts on the side thereof opposite said contact button and being pivotally mounted on said hinge pins for movement transverse of said plane, means for resiliently urging said first swivel plates toward each other and said arcing contacts into engagement with said stationary contacts, and means for resiliently urging said second swivel plates toward each other and said contact buttons into engagement with said collector ring.

3. A tap changer contact adapted to sequentially engage a plurality of coplanar stationary contacts arranged in a circle and to electrically connect said stationary contacts to a collector n'ng concentric with said circle and radially inward from said stationary contacts, said tap changer contact including at least one elongated flexible member of high electrical conductivity, a support member disposed adjacent said flexible member intermediate the ends thereof and carrying said flexible member and adapted to be moved in an arcuate path concentric with said circle, an arcing contact button secured to the radially outward end of said flexible member and a contact button secured to the radially inward end of said flexible member, a plate abutting against one end of said flexible member on the side thereof opposite said arcing contact button, means for hingedly mounting said plate on said support member for movement transverse to the plane of said stationary contacts, first means engaging said plate for resiliently urging said arcing contact button into high pressure engagement with said stationary contacts, and second means for resiliently urging said contact button into high pressure engagement with said collector ring.

4. A tap changer contact adapted to sequentially engage a plurality of coplanar stationary contacts arranged in a circle and to electrically connect said stationary contacts to a collector ring concentric with said circle and radially inward from said stationary contacts, said tap changer contact including a support member adapted to be moved in a circular path concentric with said circle about which said stationary contacts are arranged, a flexible member of high electrical conductivity, an arcing contact secured to the radially outward end of said flexible member and a contact button secured to the radially inward end thereof, a first plate-like member secured to and abutting the side of said flexible member opposite said arcing contact and a second plate-like member secured to and abutting the side of said flexible member opposite said contact button, said first and second plate-like members being pivotally mounted on said support member for movement transverse of the plane of said stationary contacts, first resilient means engaging said first plate-like member for urging said arcing contact into high pressure engagement with said stationary contacts, and second resilient means engaging said second plate-like member for urging said contact button into high pressure engagement with said collector ring.

5. A tap changer contact adapted to sequentially engage a plurality of coplanar stationary contacts arranged in a circle and to electrically connect said stationary contacts to a collector ring concentric with said circle and radially inward from said stationary contacts, said tap changer contact comprising a pair of generally radially extending, elongated flexible shunts of high electrical conductivity, a support member disposed between said shunts intermediate the ends thereof and adapted to be moved in a circle concentric with the circle about which said stationary contacts are arranged, opposed arcing contact buttons, one being secured to the radially outward end of each flexible shunt, opposed contact buttons, one being secured to the radially inward end of each flexible shunt, said shunts being carried on said support member, means for resiliently urging said arcing contact buttons toward each other and into engagement with said stationary contacts, and means for resiliently urging said contact buttons toward each other and into engagement with said collector ring.

6. A tap changer contact adapted to sequentially engage a plurality of coplanar stationary contacts arranged in a circle and to electrically connect said stationary contacts to a collector ring concentric with said circle and radially inward from said stationary contacts, said tap changer contact including a support member adapted to be moved in a circular path concentric with said circle about which said stationary contacts are arranged, a pair of opposed, generally radially extending, flexible members of high electrical conductivity disposed on opposite sides of said support member, arcing contacts secured in opposing relation to the radially outward end of said flexible members and contact buttons secured in opposing relation to the radially inward end of said flexible members, first swivel plates afiixed to the radially outward end of said flexible members on the side thereof opposite said arcing contacts and being pivotally mounted on said 'suppont member for movement transverse of the plane of said stationary contacts, second swivel plates aflixed to the radially inward end of said flexible members on the side thereof opposite said contact buttons and being pivotally mounted on said support member for movement transverse of said plane, means including a headed first pin extending axially through said first swivel plates and said flexible members and a spring surrounding said first pin and compressed between one of said first swivel plates and the head on said first pin for resiliently urging said arcing contacts against opposite sides of said stationary contacts, and means including a headed second pin extending axially through said second swivel plates and said flexible members and a spring surrounding said second pin and compressed between one of said second swivel plates and the head on said second pin for resiliently urging said contact but-tons against opposite sides of said collector ring.

7. A rotatable tap changer contact adapted to sequentially engage a plurality of coplanar stationary contacts arranged in a circle and to electrically connect said stationary contacts to a collector ring concentric with said circle and radially inward from said stationary contacts, said rotatable contact comprising a support member adapted to be moved in an arcuate path concentric with said circle, a first pair of opposed swivel plates extending radially outward from said support member and a second pair of opposed swivel plates extending radially inward from said support member, said first and second pair of swivel plates being hingedly mounted on said support member about axes parallel to the plane of said stationary contacts and tangential to circles concentric with the circle about which said stationary contacts are arranged, first and second flexible, generally radially extending shunts of high electrical conductivity carried by said support member and disposed between and abutting against said first pair of swivel plates and also disposed between and abutting against said second pair of swivel plates, opposed contact buttons on the radially outward ends of said flexible shunts and opposed contact buttons on the radially inward end of said flexible shunts, means for resiliently urging said first swivel plates and said radially outward contact buttons on said flexible shunts toward each other, and means for resiliently urging said second swivel plates and said radially inward contact buttons on said flexible shunts toward each other.

8. An electrical contact comprising a pair of generally parallel, flexible, laminated copper shunts, contact buttons on each end of said copper shunts and the corresponding contact buttons on said pair of shunts being opposed, a pair of first swivel plates and a pair of second swivel plates, a first and a second svru'vel plate being disposed adjacent the side of each copper shunt opposite to said contact buttons and being secured to said shunt adjacent the ends thereof, a pair of hinge pins disposed between said shunts and intermediate the ends thereof, each said first swivel plate being pivotally connected by one of said hinge pins to one of said second swivel plates, a support member disposed between said shunts and having apertures through which said hinge pins extend, means for resiliently urging said first swivel plates and one pair of said contact buttons toward each other, and means for resiliently urging said second swivel plates and the other pair of said contact buttons toward each other.

9. An electrical contact comprising a support member having convex surfaces on opposed sides thereof, a pair of elongated laminated flexible shunts of high electrical conductivity each having a concave portion intermediate its ends disposed against one of said convex surfaces on said support member, each shunt having a first contact button secured adjacent one end thereof and a second contact button secured adjacent the other end thereof and the contact buttons of said pair of shunts facing each other, first swivel plates secured adjacent said one end of said flexible shunts and second swivel plates secured adjacent said other end of said shunts, hinge pins extending through said support member parallel to the plane of said shunts, said first swivel plates and said second swivel plates being pivotally mounted on said hinge pins, means for resiliently urging said first swivel plates and said first contact buttons toward each other including a first pin extending through said first swivel plates transverse of said hinge pins and a spring surrounding said first pin and compressed between one of said first swivel plates and a member engaging the end of said first pin, and means for resiliently urging said second swivel plates and said second contact buttons toward each other including a second pin extending through said second swivel plates transverse of said hinge pins and a spring surrounding said second pin and compressed between one of said second swivel plates and a member engaging the end of said second pin.

10. A tap changer contact adapted to sequentially engage a plurality of coplanar stationary contacts arranged in a circle and to electrically connect said stationary contacts to a collector ring concentric with said circle and radially inward from said stationary contacts, said tap changer contact including a support member adapted to be moved in a circular path concentric with said circle about which said stationary contacts are arranged, at least one elongated generally radially extending laminated fiexible shunt of high electrical conductivity comprising a fiat- -tened continuous spiral of copper strip carried by said References Cited in the file of this patent UNITED STATES PATENTS 1,831,843 Cornfield Nov. 17, 1931 1,863,392 Brand et a1 June 14, 1932 1,956,026 Heinrich Apr. 24, 1934 2,363,866 McKenney Nov. 28, 1944 2,662,130 Sealey Dec. 8, 1953 2,686,236 Hodtum Aug. 10, 1954 2,693,573 Perkins Nov. 2, 1954 2,785,242 White Mar. 12, 1957 FOREIGN PATENTS 476,941 France Sept. 9, 1915 376,108 Germany May 24, 1923 405,424 Great Britain Feb. 8, 1934 1,175,163 France Mar. 20, 1959 

